It's up to parents to take immediate action: As the saying goes, "get them up off the seats and out on the streets."

Considering the great strides in medical and nutritional science reported almost daily in the media, most of us expect our children to live healthier, longer lives than us. Indeed, throughout human history, that has been the norm - each generation has lived longer than the previous one. Unless we take immediate and drastic action, however, that trend is about to reverse.

The University of South Australia's global research project on child fitness makes disquieting reading. The research findings, released at The American Heart Association's annual meeting in November 2013, show that when today's parents and grandparents were children, they were significantly fitter than children are now. The researchers examined 50 studies on running endurance - a reliable measure of cardiovascular fitness - carried out between 1964 and 2010 on more than 25 million children aged between nine and seventeen from 28 mostly rich countries. They compared cardiovascular fitness figures and found that children today are, on average, 15% less fit than their parents were at the same age. That means, for example, that children today take about 90 seconds longer to run a mile than their parents did in 1975. In fact, children's endurance fell by an average of 5% per decade between 1970 and 2000. The figure for the US was 6%.

Extrapolating the data forward, the researchers estimate that in later life these children will be more susceptible to many serious illnesses like heart disease and strokes, and will die younger than the previous generation. Advances in medical and nutritional sciences will not counteract the damage caused by unhealthy lifestyles.

Parents, however, are perfectly placed not only to counteract the damage, but also to prevent it from happening in the first place. The solution is to introduce a lifestyle modification plan for their children. It should include these three elements:

. More exercise. Children should exercise for at least one hour each day. They can do it in a few brief sessions or in one longer session. Most physical activities are suitable as long as they mainly exercise the body's big muscles and increase the heart rate. Swimming and running are ideal, but cycling or brisk walking can also be part of the regime. Crucially, they must do it every day.

. Less sitting. Regular, prolonged sitting is harmful, even if children exercise for an hour a day. According to Professor Francois Carré, sport cardiologist at the University of Rennes in France, prolonged sitting promotes inflammation, oxidative stress, and unhealthy cholesterol levels, and increases the risk of developing diabetes and hypertension. "We have known since the 1990s that the more time you spend sitting, the less long you are likely to live," he told Le Figaro Newspaper, when asked about the Australian research.

. Diet. Most store-prepared meals, fast foods, and sugary drinks are not just nutritionally deficient, but are packed with substances like saturated fat, sodium chloride (table salt), and sugar, which are unhealthy, even in relatively small quantities. Young people should avoid such food, and instead, eat a balanced diet rich in fresh vegetables, fresh fruit, cereals, fish and poultry. Ideally, all their meals should be prepared and cooked at home.

None of this is very surprising. Many young people lead sedentary lifestyles; some are obviously overweight. Unlike their parents when they were young, many are driven to and from school. After school, they spend hours on their smartphones, computers, video consoles, and watching television. Only their fingers get any exercise.

It's up to parents to take immediate action: As the saying goes, "get them up off the seats and out on the streets." If today's mothers and fathers do nothing, they could well outlive their own children. That is hardly the way Mother Nature intended it.